1. Field of the Invention
This invention relates to machines for a two-dimensional depiction of the sun's daily path and for information on sunlight, such as the times of sunrise and sunset and solar energy.
2. Description of the Prior Art
Understanding how the sun's apparent motion and sunlight change with location, season, and time is of interest for basic knowledge, science education, and practical use. Machines can be built to aid the understanding, based on the known fact that these five quantities are interrelated: the sun's angular height, the sun's direction, latitude, date, and sun time, which is independent of longitude and is 12 noon when the sun is highest in a day. Any three of the five quantities determine the remaining two.
Armillary spheres of antiquity composed of rotatable rings have the capability of demonstrating the sun's daily path and indicating the sun's angular height and direction, for any latitude, date, and time.
Computers and other electrical machines can also achieve said capability but cannot directly reveal how they function.
Comparing with armillary spheres and electrical machines, flat, two-dimensional and nonelectrical machines with said capability seem to be potentially less costly, more portable, and more direct in disclosing their working principle. Yet no flat machine with said capability is found described in the prior art. For example, U.S. Pat. No. 4,083,121, issued Apr. 11, 1978, describes a planisphere for stars but not for the sun's angular height and direction. U.K. Patent No. 8,923, accepted Nov. 20, 1913, describes a flat machine that gives the times of sunrise and sunset but again does not give the sun's angular height and direction The following three patents have some of said capability, in narrowed scopes.
U.S. Pat. No. 2,440,827, issued May 4, 1948, and No. 2,715,273, issued Aug. 16, 1955, describe a flat machine that applies to all dates but for only a fixed latitude, depicts a plan view of the sun's daily path, as a curve. The shape of the curve varies with date and latitude. U.S. Pat. No 990,764, issued Apr. 25, 1911 and titled Sun-Path Dial, describes a flat machine that applies to all latitudes but for only four fixed dates, depicts an elevation view of the sun's daily path as a straight line.
The present invention applies to all latitudes and dates by overcoming the following difficulties of the prior art.
The elevation view of the sun's daily path, as a straight line, shows the sun's angular height but conceals the sun's direction. It is unobvious how to find the sun's direction from the elevation view. It is also unobvious for a machine to give more information than the three patents last cited and yet not to appear crowded with lines, numbers, and other markings. It is again unobvious how to design components, of such a machine and how to fit them together. It is further unobvious that such a machine can be homemade from pieces of paper with needed markings, transparent sheets marked with only a few straight lines, and easily available material, such as card board and a thumb tack.
A recent Italian paper, "Percorso apparente del Sole nel cielo locale", Geofisco vol. 29, no. 1, pp 39-51 (1988) by C. Bernasconi, explains how to calculate the sun's angular height and direction and tabulates such sunlight information for only selected latitudes, dates, and times. This recent paper indicates that such sunlight information, readily obtainable from the present invention, is of interest but not yet readily available.